When interacting with Azure Blob Storage via the Hadoop FileSystem client, it's currently (as of a8bbd81) not possible to set custom metadata attributes.
Here is a snippet that demonstrates the missing behavior (throws an UnsupportedOperationException):
Looking at the code in hadoop-tools/hadoop-azure, NativeAzureFileSystem inherits the default setXAttr from FileSystem which throws the UnsupportedOperationException.
Is there another way that I should be setting custom metadata on Azure Blob Storage files? Is there a specific reason why setXAttr hasn't been implemented on NativeAzureFileSystem? If not, I can take a shot at implementing it.